Search

La0.7Ca0.3Mn0.5Fe0.5O3(LCMFO) ceramic samples were prepared by conventional solid-state reaction. X-Ray diffraction investigations show that samples have orthorhombic space group Pnma (a = 5.447(2) Ǻ, b = 7.709(3) Ǻ, c = 5.467(3) Ǻ). During the neutron powder diffraction measurements of LCMFO in the temperature range of 10 ÷ 300 K the antiferromagnetic long-range ordering of G-type was seen. It has been established that 50% substitution of Mn/Fe leads to a complete suppression of the ferromagnetism in LCMFO samples. Investigations of temperature dependence of the magnetization, M(T), suggests the frustration of magnetic ground state and the existence of a spin-glass or a cluster-glass phase below the magnetic transition temperature close to 350 K. The temperature dependences of conductivity for La0.7Ca0.3Mn0.5Fe0.5O3sample investigated in magnetic fields B = 0 and 1 T. According to the research, the mechanisms of hopping conductivity were established. Micro parameters in density of localized states were calculated for LCMFO samples. The width of the Coulomb gap Δ = 0.67 eV, rigid gap δ = 0.324 eV and the localization radii of charge carriers were estimated. [ABSTRACT FROM PUBLISHER]

The crystal and magnetic structure of nanostructured manganites La 0.63 Sr 0.37 MnO 3 and La 0.72 Sr 0.28 MnO 3 has been studied by means of a neutron diffraction method in the pressure range 0–4.5 GPa and the temperature range 5–300 K. In both samples the FM ordering is formed close above the room temperature and at cooling below T < 270 K the ferromagnetic FM phase coexists with an A-type antiferromagnetic AFM phase. At high pressures the volume fraction of AFM phase increases, while FM is gradually suppressed. The structural aspects of the magnetic phase separation and pressure effects on the studied nanostructured manganites are discussed. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structure of the nanostructured manganite La 0.53 Sr 0.47 MnO 3 has been studied using the neutron diffraction method in the pressure range 0–5.5 GPa and the temperature range 15–300 K. At ambient pressure, the ferromagnetic ordering in the studied compound is formed below T ≈ 335 K. With an increase of the pressure above 2.1 GPa and cooling below T < 250 K, an A-type antiferromagnetic phase appears, which coexists with the initial ferromagnetic one. Further increase of the pressure leads to the growth of the volume fraction of the antiferromagnetic phase, while the ferromagnetic ordering is gradually suppressed. The structural origins of the pressure-induced magnetic phase separation in the nanostructured manganites are discussed. • The structure of nanomanganite La0.53Sr0.47MnO3 at high pressure have been studied. • The FM ordering in this compound was formed at ambient pressure, below T ≈ 335K. • At P ≥ 2.1 GPa and T < 250 K, the coexistence of FM and A-type AFM phase was found. • The structural separation was discussed in the framework of the "core-shell" model. • The most important parameters of crystal and magnetic structures were calculated. [ABSTRACT FROM AUTHOR]

A novel metastable phase of DyGe 2.85 synthesised in the AuCu 3 -structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P ≤ 3.1 GPa), neutron powder diffraction and time-differential γ - γ perturbed angular correlations (TDPAC) using 111 Cd nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature T CDW = 80 K with charge density wave formation and the second transition at T N ≈ 18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of Cr 2 O 3 have been studied by means of X-ray and neutron powder diffraction at high pressures up to 35 GPa. The lattice compression of the rhombohedral crystal structure of R 3 ¯ c symmetry is slightly anisotropic with anomaly in the pressure behavior of the c/a parameters ratio at P ≈ 20 GPa of presumably magnetic nature. The oxygen octahedra around chromium ions become more symmetric with close values of shared and unshared bonds under high pressure. The antiferromagnetic structure of Cr 2 O 3 remains stable in the studied pressure range up to 35 GPa. The pressure coefficient of the Néel temperature, (1/ T N )( dT N /dP ) = + 0.0091 GPa −1 , is significantly less in comparison with perovskite-like compounds containing Cr 3+ and Mn 4+ ions of similar electronic configuration. [ABSTRACT FROM AUTHOR]

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO 3 have been studied by means of neutron, X-ray powder diffraction and Raman spectroscopy at pressures up to 6.2 and 42 GPa, respectively. A presence of Fe/Ga antisite disorder leads to a formation of the ferrimagnetic ground state with the Néel temperature T N = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Néel temperature increases with a pressure coefficient (1/T N )(dT N /dP) = 0.011(1) GPa −1 . Application of high pressure above 21 GPa leads to a gradual structural phase transition from the polar orthorhombic Pc 2 1 n phase to nonpolar orthorhombic Pbnm phase. It is accompanied by anomalies in the pressure behaviour of several Raman modes. Pressure dependencies of lattice parameters and Raman modes frequencies in the observed structural phases were obtained. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structure of a manganite La 0.7 Sr 0.3 Mn 0.83 Nb 0.17 O 3 have been studied by means of a neutron diffraction method at pressures up to 4.5 GPa and in temperature range 4–290 K. At ambient pressure and temperature below T C = 150 K a ferromagnetic FM state is stabilized in this compound. At pressures P ≥ 1.5 GPa and temperature below T N ∼110 K appearance of a new A-type antiferromagnetic AFM phase in La 0.7 Sr 0.3 Mn 0.83 Nb 0.17 O 3 has been observed. A further pressure increasing leads to an increase in the volume fraction of the A-type antiferromagnetic AFM phase, which coexists with the suppressed ferromagnetic phase in the whole experimental pressure range. The Curie and Néel temperature increase upon lattice contraction with comparable pressure coefficients dT C /dP = 2.1 K/GPa and dT N /dP = 1.6 K/GPa. The structural mechanisms of the changes in magnetic structure of La 0.7 Sr 0.3 Mn 0.83 Nb 0.17 O 3 manganite are discussed. [ABSTRACT FROM AUTHOR]

We had investigated the pressure-induced phase transition phenomenon in the perovskite-like material Nd 2 Ti 2 O 7 compound. The structural and vibrational properties of a layered Nd 2 Ti 2 O 7 have been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 30 GPa. The gradual structural phase transition from the initial monoclinic P2 1 C 2 2 phase to the monoclinic P2 C 2 1 phase was observed at P ∼ 19 GPa. This pressure-induced phase transition is accompanied by anomalies in the pressure behavior of unit cell parameters and vibrational modes. The role of pressure application as a trigger for a significant rotation of the TiO 6 octahedra, alterations in interatomic distances, and the displacement of Nd atoms were discussed. • Structural and vibration properties of perovskite-like layered Nd 2 Ti 2 O 7 was studied at pressures up to 30 GPa. • The structural phase transition in Nd 2 Ti 2 O 7 was observed at P = 19.2 GPa. • The suppression of the ferroelectric phase of Nd 2 Ti 2 O 7 was discussed. • The bulk modulus of both phases were calculated. [ABSTRACT FROM AUTHOR]

Highlights • The magnetic properties of ordered double perovskite Pb 2 FeSbO 6 were studied in details. • Unexpected long-range antiferromagnetic ordering in Pb 2 FeSbO 6 compound was found. • The antiferromagnetic phase in Pb 2 FeSbO 6 formed on the cation disordering structural domains. • The propagation vector of the antiferromagnetic phase is q = (½, ½, 0). • Under cooling, the structural phase transition in Pb 2 FeSbO 6 occurs. Abstract The structural and magnetic ordering of Pb 2 FeSbO 6 was studied by means of Mössbauer spectroscopy and neutron powder diffraction in the temperature range from 5 to 300 K. The structural phase transition from the initial cubic phase Fm 3 ¯ m to the tetragonal I 4 / m phase was observed in temperature range 170–190 K. The antiferromagnetic order with a propagation vector q = (½, ½, 0) was found at temperature T < T N = 30 K. The temperature dependences of the hyperfine parameters of Mössbauer spectra and magnetic moments for Pb 2 FeSbO 6 at low temperatures were obtained. The relationships between the short-range cation ordering observed by Mossbauer spectroscopy and the long-range cation ordering observed by neutron powder diffraction are discussed. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structures of La 0.7 Ca 0.3 Mn 0.5 Fe 0.5 O 3 compound have been studied by neutron powder diffraction in the temperature range of 10–300 К. The magnetization and electrical resistivity measurements have been also performed in the temperature range of 5–300 K in magnetic fields up to 1 T. These experimental results indicate a formation of a complex magnetic state in which the long-range antiferromagnetic G-type phase coexists with the short-range ferromagnetic clusters. The electrical conductivity of La 0.7 Ca 0.3 Mn 0.5 Fe 0.5 O 3 demonstrates an anomalous temperature behavior suggesting a switching between different states. The origin of the unconventional magnetic state, the mechanisms of the electrical conductivity, and correlation between magnetic and transport properties in this manganite have been discussed. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of DyCo 2 compound were studied at pressures p ≤ 5.6 GPa, in the temperature range 4–300 K, by neutron diffraction. In addition, magnetic measurements and band structure calculations were performed. The pressure dependence of the cobalt moments, experimentally determined, agree well with the calculated values. An isomorphic structure transition, parallelly with the collapse of cobalt moments, has been evidenced. The physical mechanisms involved in describing the pressure effects on the DyCo 2 magnetic properties are analysed. [ABSTRACT FROM AUTHOR]

The structural, magnetic and vibrational properties of the BaMn 1- x Ti x O 3 system (0 ≤ x ≤ 0.25) have been studied by X-ray and neutron powder diffraction, electron spin resonance (ESR) and Raman spectroscopy methods. A sequence of the structural phase transitions 15R → 8H → 9R → 10H → 12R was observed upon Ti doping. The structural parameters of the observed phases were determined. Antiferromagnetic ordering in the 15R, 9R and 8H structural phases was observed at low temperatures. The magnetic propagation vector is q = (0 0 1/2) for the 15R and 9R phases and q = (0 0 0) for the 8H phase. The magnetic ordering temperatures and the ordered Mn magnetic moments are suppressed rapidly with increase of the Ti concentration from T N = 230 ( x = 0) to 100 K ( x = 0.25) and m = 2.0 to 1.2 μ B , respectively. The relationship between the Raman spectra of different structural phases of BaMn 1- x Ti x O 3 and concentration dependencies of the vibrational modes were analyzed. [ABSTRACT FROM AUTHOR]

• A significant suppression of the ordered magnetic moment at high pressure is observed, associated with enhancement of spin fluctuations. • The pressure increase of Neel temperature is more pronounced with respect to other hexagonal RMnO 3 compounds. • A change of the ground magnetic state symmetry from mixed Г 1 + Г 2 to pure Г 1 irreducible representation is expected at pressure of about 6 GPa. The crystal and magnetic structures of hexagonal manganite ScMnO 3 have been studied by means of neutron diffraction at high pressures up to 2 GPa in the temperature range 10–300 К. At ambient pressure below T N = 130 K the triangular antiferromagnetic (AFM) state of mixed Г 1 + Г 2 irreducible representation is formed. Upon application of high pressure, the symmetry of magnetic structure persists up to 2 GPa. A significant suppression of the ordered magnetic moment and gradual spin reorientation were revealed under pressure. The baric dependence of Neel temperatures T N was obtained with the average linear pressure coefficient dT N / d P = 6.9 K/GPa, which is significantly larger with respect to related compounds like YMnO 3. For the data obtained, one may expect modification of the magnetic ground state symmetry to the pure Г 1 representation at pressures about 6 GPa. [ABSTRACT FROM AUTHOR]

Neutron diffraction measurements were made under pressure on Ca 1.5 La 0.5 FeMoO 6 double perovskite. The monoclinic P2 1 /n structure remains stable up to 5.7 GPa. The ordered magnetic moments at B(Fe) sites increase with pressure, while those at B′(Mo) ones are nearly pressure independent. The magnetic properties determined by neutron diffraction, at normal pressure, are compared with those obtained from magnetic measurements. The sites occupancies and valence states of Fe and Mo cations, when increasing pressure, have been analysed and correlated with the structure parameters. [ABSTRACT FROM AUTHOR]

The Ca 1.5 La 0.5 FeMo 1 − x W x O 6 double perovskites with x ⩽ 0.3 crystallize in a monoclinic structure having space group P2 1 /n. The degree of crystallographic ordering is increased as the tungsten content is higher. As a result, there is an increase of both saturation magnetizations and Curie temperatures. The magnetic susceptibilities follow temperature dependences typical for a ferrimagnetic system. The valence states of iron and molybdenum ions as well their distributions in the lattice sites were determined. These data were correlated with magnetic and transport properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] The detailed P–T phase diagram of BiMnO3 was established. [•] We found three monoclinic modifications of BiMnO3 at pressure and temperature. [•] A suppression of monoclinic C2/c phase have been observed under pressure. [•] We found a new orthorhombic Imma phase of BiMnO3 at P >20GPa. [Copyright &y& Elsevier]

Abstract: The crystal structure and magnetic properties of TbCo2 compound have been analyzed by neutron diffraction, at pressures up to 4.1GPa in the temperature range 10–300K. A rhombohedral type structure of type is shown below Curie temperature. The distortion degree of structure increases with pressure as well as when lowering temperature. The temperature dependences of terbium and cobalt moments can be described by Brillouin functions. The Curie temperatures decrease linearly with pressure with a slope of dTc /dP =−9K/GPa. The evolution with pressure of the cobalt magnetic moments and Tb5d band polarizations are theoretically analyzed. The experimental data are well described by band structure calculations. The magnetic behavior of cobalt in heavy rare-earth RCo2 compounds is analyzed in spin fluctuations model. A gradual quenching of spin fluctuations by internal field was shown. [Copyright &y& Elsevier]

• A phase coexistence of hcp and Sm-type phases is found in 160Gd at ambient conditions. • The hcp phase and FM order are rapidly suppressed under pressure. • In the Sm-type phase, stabilized by pressure, the AFM order is formed. Structural and magnetic properties of the isotopically substituted 160Gd metal (97.5 % enrichment) were studied by means of neutron powder diffraction at pressures up to 9 GPa in the temperature range 7 – 290 K. At ambient conditions, a coexistence of hexagonal close packed (hcp) and Sm-type rhombohedral phases was observed. Under high pressure, the hcp phase was suppressed gradually and above 6 GPa only the Sm-type phase is observed. The long range ferromagnetic order formed in the hcp phase is also suppressed rapidly with a pressure coefficient of the Curie temperature dT C /dP = -6.3(1) K/GPa. In the Sm-type phase below the Néel temperature of about 100 K (evaluated for 9 GPa), the long range antiferromagnetic order with a propagation vector k AF = (0 0 1/2) is formed. The lattice parameters and unit cell volume as functions of pressure in the hcp and Sm-type phases were determined. A partial phase transformation of the Sm-type phase to the double hexagonal close packed (dhcp) phase was observed at 9 GPa. [ABSTRACT FROM AUTHOR]

• Magnetically disordered phase is suppressed under pressure. • The Néel temperature increases substantially under pressure. • The mechanism of next nearest neighbor superexchange interactions of A-O-O-A type is proposed. The crystal and magnetic structures of the frustrated Co 3 O 4 spinel oxide have been studied by means of neutron diffraction at high pressures up to 8.7 GPa in the temperature range 5–300 K. At ambient pressure, a coexistence of the long range ordered antiferromagnetic (AFM) phase and short range disordered phase below T N = 33 K was observed. At pressures above 2 GPa, a suppression of the magnetically disordered phase and stabilization of the AFM phase, characterized by rapid increase of the Néel temperature in 1.5 times from 33 to 51 K with a pressure coefficient dT N /dP = 2.1 K/GPa occur. The observed phenomena are analyzed in terms of the competing nearest neighbor and next nearest neighbor magnetic interactions. In addition to the A-O-B-O-A nearest neighbor superexchange, an important role of the A-O-O-A next nearest neighbor superexchange interactions in magnetic behavior of Co 3 O 4 is pointed out. [ABSTRACT FROM AUTHOR]

We report a systematical investigation of the structural, magnetic, electronic, and dielectric properties of BaFe 1- x Ti x O 3- δ (x = 0.05, 0.10, 0.15 and 0.20) samples synthesized via the solid-state reaction method. Rietveld refinement using a combination of room-temperature X-ray (XRD) and neutron powder diffraction (NPD) data confirms single phases with a 6H-type structure for all the samples. X-ray absorption spectroscopy (XAS) study reveals a coexistence of Fe3+ and Fe4+, whose ratio remains almost unchanged with increasing Ti concentration. Magnetization measurements reveal a low-temperature inhomogeneous magnetic state with coexisting ferromagnetic (FM), AFM clusters and a paramagnetic phase. Moreover, magnetization of x = 0.10 shows a pinched hysteresis loop behavior, suggesting the coexistence of hard and soft FM phases in samples with high Ti concentrations. Low-temperature NPD measurements also confirm the absence of any long-range magnetic order in the samples. A colossal dielectric permittivity and two relaxation processes are observed for most of the studied samples. There is a change in electric conduction mechanism from the small polaron hopping to the Mott's variable-range hopping with increasing Ti concentration. • 6H-type Ti-doped BaFeO 3- δ exhibit colossal dielectric permittivity. • Interfacial Maxwell-Wagner polarization effect at grain boundaries is the origin of the colossal dielectric permittivity. • Change in the electrical conduction mechanism upon increasing Ti-doping level. • Ti doping destroys the helical antiferromagnetic long-range order of the undoped BaFeO 3. • Complex inhomogeneous magnetic state with coexistence of cluster-glass and paramagnetic phases. [ABSTRACT FROM AUTHOR]